Exhaust gas recirculation (EGR) is used to reduce pollution generated by engines and other combustion devices. EGR strategies reduce the oxygen content of the intake air charge by diluting it with an inert gas, such as exhaust. When the diluted air-exhaust mixture is used in place of ordinary air to support combustion in the engine, lower combustion and exhaust temperatures result. EGR also improves fuel economy in gasoline engines by reducing throttling losses and heat rejection.
With EGR, a portion of the exhaust gas generated by the engine is mixed into the air intake. Mixers typically add exhaust gas to the air flow somewhere in the middle of the air stream and rely on length or geometric features, such as bumps of fins, to induce mixing. These typical air-exhaust mixer assemblies occupy a large amount of space so as to ensure that the exhaust gas and intake air are completely mixed. Incomplete mixing of the air and exhaust gases can lead to an uneven distribution of EGR among the cylinders. To ensure complete mixing of the gases, typical venturi type mixers have long mixing cavities. An intake throttle may be used in some cases to increase the pressure differential between the EGR gas and the compressed fresh air. Other types of mixers have mixing cavities with large lengths, widths and/or heights in order ensure complete mixing of the gases. These large mixers in turn make retrofitting of air-exhaust mixers to engines quite expensive, because the plumbing of the engine has to be extensively modified in order to accommodate the large air-exhaust mixers. Another problem is that larger mixers significantly reduce the pressure of the mixed gas supplied to the engine.
Engines and diesel engines in particular, can benefit from EGR mixers which promote the maximum amount of mixing while causing the least amount of restriction possible in both the EGR and the air circuits. Mixing is necessary to ensure that there is as little variation as possible in EGR content from cylinder to cylinder that could cause poor emissions and performance results. Efficient mixing often results in increases in gas flow restrictions. Restrictions in either of the EGR or fresh air passages can result in reduced fuel economy.
The present device provides a compact venturi mixer, which overcomes the above disadvantages by providing an enhanced mixing feature. The present device promotes a maximum amount of mixing between the EGR gases and fresh air, while causing the least amount of restriction possible in both the EGR exhaust gas flow and fresh air flow.